Evaluation and control unit for a gas sensor

ABSTRACT

An evaluation and control unit ( 100 ) for a broadband lambda probe ( 200 ) and a method for operating the same are disclosed. The evaluation and control unit ( 100 ) comprises pins (RE, IPE, APE, MES) connectable to electrical wires ( 201, 202, 203, 204 ) of electrochemical cells ( 210, 211 ) of the broadband lambda probe ( 200 ), a controller ( 103 ), a ASIC reference potential source ( 102 ), wherein the ASIC reference potential source ( 102 ) is operable by means of the controller ( 103 ), a switch assembly ( 104 ) connected to each of the pins (RE, I PE, APE, MES), wherein the switch assembly ( 104 ) comprises a first transistor (T Wire ) and a second transistor (T ECU ), wherein the switch reference potential source ( 105 ) is connected to a gate side of the first and second transistors (T Wire , T ECU ), wherein the controller ( 103 ) is configured to vary the switch reference potential (V SW ) applied to the gate side of the first and second transistors (T Wire , T ECU ), wherein the switch assembly ( 104 ) is configured to allow a limiting current flowing to the drain side of the first transistor (T Wire ) from the ASIC reference potential if the potential at the gate side of the first and second transistors (T Wire , T ECU ) is at a predetermined voltage between values of an open and closed switch.

PRIOR ART

In order to detect characteristics of gases, several sensor types areknown. One example is a lambda probe which is used to detectcharacteristics of the exhaust of an internal combustion engine. Suchlambda sensors or probes are known from Konrad Reif (Hrsg.): Sensoren imKraftfahrzeug, 1. edition 2010, pages 160-165, for example.

A control unit for the operation of a broadband lambda probe isdescribed in German Patent Application No. DE 10 2008 001 697 A1.“Operation” encompasses in particular control of the lambda probe, aswell as evaluation of the signals or data supplied by the lambda probe.The control unit encompasses a signal conditioning unit, ananalog/digital (A/D) converter, a pump current controller, a digitalinterface, a controller, a pump current source, an internal pumpelectrode terminal, an external pump electrode terminal, and a referenceelectrode terminal. The signal conditioning unit is provided in order toascertain an actual value for the pump current controller, and toascertain further information regarding the operating state of thebroadband lambda probe. The further information regarding the operatingstate of the broadband lambda probe is outputtable via the digitalinterface. A corresponding control unit, in the form of an integratedcircuit (IC) for controlling broadband lambda probes suitable for dieseland gasoline engines, is marketed by the Applicant under the designation“CJ135”.

A plurality of further control units specialized for a particularapplication are encountered nowadays in internal combustion engines orin motor vehicles equipped with such internal combustion engines. Aninternal combustion engine is furthermore operated, in a conventionalmanner, by way of an engine control device. These control units orcontrol devices possess analog and digital inputs that in part alsoprovide additional functions such as a pull-up/pull-down structure, or avoltage divider required, for example, for the evaluation of temperaturesensors. The evaluation circuits on which these are based can be made upof discrete components or, by combining multiple inputs and outputs, ofindividual application-specific integrated circuits (ASICs).

The semiconductor building-up the ASIC only works in a certain voltagerange. Outside this voltage range, structures meant to be insulating canbecome conducting or permanently damaged. Below the lowest voltage, i.e.its ground voltage, the structure has to be protected, hindering itsoriginal functionality. In particular, such a structure for operating awide band lambda sensor as described in DE 10 2011 007 068 A1 is knownfrom DE 10 2010 000 663 A1 or EP 2 277 035 B1, which contains wireselectrically connected to the evaluation and control units. Currently,diagnosis of the electrical wires of the wide band lambda sensor are notcomplete with respect to the detection of short circuits. Attempts havebeen made to improve especially the pin-pointing of the diagnosis suchas described in US2013/0234744 A1.

Despite the advantages provided by the above devices and methods fordetecting short circuits, there is still potential for improvements.Particularly, the above devices and methods have so far proved not to berobust. Especially detection of short circuit to voltages below the ECUground voltage are incomplete due to the limitation of the technologymentioned above. Such voltages can appear at usually short circuit toground demonstration, since there the wire is connected to the ground ofthe vehicle. It differs from the ECU ground voltage of the ASIC due toleakage currents from other components and the spatial distance betweenECU and the vehicle ground connection. In case a short circuit to groundis applied, i.e. a low out-of-range fault, the analysis withconventional devices is hindered by the wish to protect the internalhardware. In particular, for cold sensors the ECU only needs to beprotected against voltages at the wire, where the short circuit pin isapplied. However, due to couplings between the wires, e.g. by capacitorsor former warm sensor, similar voltages exists at each wire. Thus,typically all wires are disconnected from the evaluation circuit. Incontrast to the direct short circuit connection, these coupling effectscan be temporary with the proper circuitry. Nevertheless, they hinder topin-point the short circuit to the corresponding wire due to theactivated common hardware protection.

SUMMARY

Thus, an evaluation and control unit for a gas sensor, particularly abroadband lambda probe, and a method for operating the same aredisclosed which aim to reduce the disadvantages provided by the abovedescribed devices and methods and which particularly allow for apin-pointing to UEGO (Universal Exhaust Gas Oxygen) signal wire specificentries.

As used in the following, the terms “have”, “comprise” or “include” orany arbitrary grammatical variations thereof are used in a non-exclusiveway. Thus, these terms may both refer to a situation in which, besidesthe feature introduced by these terms, no further features are presentin the entity described in this context and to a situation in which oneor more further features are present. As an example, the expressions “Ahas B”, “A comprises B” and “A includes B” may both refer to a situationin which, besides B, no other element is present in A (i.e. a situationin which A solely and exclusively consists of B) and to a situation inwhich, besides B, one or more further elements are present in entity A,such as element C, elements C and D or even further elements.

Further, it shall be noted that the terms “at least one”, “one or more”or similar expressions indicating that a feature or element may bepresent once or more than once typically will be used only once whenintroducing the respective feature or element. In the following, in mostcases, when referring to the respective feature or element, theexpressions “at least one” or “one or more” will not be repeated,non-withstanding the fact that the respective feature or element may bepresent once or more than once.

Further, as used in the following, the terms “preferably”, “morepreferably”, “particularly”, “more particularly”, “specifically”, “morespecifically” or similar terms are used in conjunction with optionalfeatures, without restricting alternative possibilities. Thus, featuresintroduced by these terms are optional features and are not intended torestrict the scope of the claims in any way. The invention may, as theskilled person will recognize, be performed by using alternativefeatures. Similarly, features introduced by “in an embodiment of theinvention” or similar expressions are intended to be optional features,without any restriction regarding alternative embodiments of theinvention, without any restrictions regarding the scope of the inventionand without any restriction regarding the possibility of combining thefeatures introduced in such way with other optional or non-optionalfeatures of the invention.

The control and evaluation unit according to the present invention,preferably embodied as an ASIC, is universally usable for the operationand evaluation of a gas sensor such as a broadband lambda probe.Nevertheless, the control and evaluation unit as disclosed herein isapplicable to any type of gas sensor such as a NOx-sensor. The controland evaluation unit comprises pins connectable to electrical wires ofelectrochemical cells of the gas sensor, a controller, an ASIC referencesource, wherein the ASIC reference source is operable by means of thecontroller, a switch assembly connected to each of the pins, wherein theswitch assembly comprises at least a first transistor, wherein a switchreference source is connected to a gate side of the first transistor andthe ASIC reference source is connected to the source side of the firsttransistor, wherein the controller is configured to vary a switchreference potential applied to the gate side of the first transistor,wherein the switch assembly is configured to allow a limited currentflowing to the drain side of the first transistor from the ASICreference source if the potential at the gate side of the firsttransistor is at a predetermined voltage between values of an open andclosed switch over the potential at the source side of the firsttransistor.

The ASIC reference source and or the switch reference source may be apotential source or a current source.

The controller may be configured to switch the ASIC reference potentialprovided by the ASIC reference source to a value larger than the groundof the controller while the switch assembly is in an open state.

The controller may be configured to put the first transistor in a linearmode by varying the switch reference potential in relation to a sourcepotential of the first transistor.

The term “linear mode” as used herein may refer to a mode of atransistor wherein it is neither fully conducting nor fully open, butacts as a current source or a very high resistance. This means it allowsa flowing current, which is much smaller as it would be in theconducting state. Particularly, in the linear mode current isindependent from drain-source voltage. This enables of charging ordischarging externally structures like capacitors with time.

The evaluation and control unit may further comprise at least onecomparator, wherein the controller may be configured put the switchassembly in an open state if a short circuit to ground is detected bythe comparator.

The comparator may be configured to detect a short circuit to groundpresence or absence at one of the pins if the ASIC reference potentialis raised and a potential at that pin exceeds a comparator threshold.If, at one of the pins when the ASIC reference potential is raised, thepotential at that pin exceeds a comparator threshold, a short circuit toground is present. Particularly, if the ASIC reference potential israised, some comparators will show that there is short-circuit to groundbut other comparators will show that there is no short-circuit.

The switch assembly may further comprise a second transistor, whereinthe switch reference source is connected to a gate side of the secondtransistor and the ASIC reference source is connected to the source sideof the second transistor.

The method for operating an evaluation and control unit according to thepresent invention comprises the following steps:

varying the switch reference potential applied to the gate side of thefirst transistor, in order to allow a limited current flowing to thedrain side of the first transistor from the ASIC reference source if thepotential at the gate side of the first transistor is at a predeterminedvalue between values of an open and closed switch over the potential atthe source side of the first transistor.

The method may further comprise switching the ASIC reference potentialto a value larger than the ground of the controller while the switchassembly is in an open state.

The method may further comprise putting the first transistor in a linearmode by varying the switch reference potential in relation to a sourcepotential of the first transistor.

The method may further comprise detecting a short circuit to groundpresence or absence by means of at least one comparator and putting theswitch assembly in an open state if the short circuit to ground at oneof the pins is detected.

The method may further comprise raising the ASIC reference potential anddetecting a potential at one of the pins, wherein a short circuit toground presence or absence is detected. If, at one of the pins when theASIC reference potential is raised, the potential at that pin exceeds acomparator threshold, a short circuit to ground is present.Particularly, if the ASIC reference potential is raised, somecomparators will show that there is short-circuit to ground but othercomparators will show that there is no short-circuit.

Further, a computer program is disclosed that is configured to carry outeach of the steps of the method.

Further, an electronic storage device is disclosed, on which such acomputer program is stored.

Furthermore, an electronic control unit is disclosed which comprisessuch an electronic storage device.

The present disclosure further discloses and proposes a computer programincluding computer-executable instructions for performing the methodaccording to the disclosed method/device/system in one or more of theembodiments enclosed herein when the program is executed on a computeror computer network. Specifically, the computer program may be stored ona computer-readable data carrier. Thus, specifically, one, more than oneor even all of the method steps as indicated above may be performed byusing a computer or a computer network, preferably by using a computerprogram.

The present disclosure further discloses and proposes a computer programproduct having program code means, in order to perform the methodaccording to the disclosed method/system in one or more of theembodiments enclosed herein when the program is executed on a computeror computer network. Specifically, the program code means may be storedon a computer-readable data carrier.

Further, the present disclosure discloses and proposes a data carrierhaving a data structure stored thereon, which, after loading into acomputer or computer network, such as into a working memory or mainmemory of the computer or computer network, may execute the methodaccording to one or more of the embodiments disclosed herein.

The present disclosure further proposes and discloses a computer programproduct with program code means stored on a machine-readable carrier, inorder to perform the method according to one or more of the embodimentsdisclosed herein, when the program is executed on a computer or computernetwork. As used herein, a computer program product refers to theprogram as a tradable product. The product may generally exist in anarbitrary format, such as in a paper format, or on a computer-readabledata carrier. Specifically, the computer program product may bedistributed over a data network.

Finally, the present disclosure proposes and discloses a modulated datasignal which contains instructions readable by a computer system orcomputer network, for performing the method according to one or more ofthe embodiments disclosed herein.

Preferably, referring to the computer-implemented aspects of theinvention, one or more of the method steps or even all of the methodsteps of the method according to one or more of the embodimentsdisclosed herein may be performed by using a computer or computernetwork. Thus, generally, any of the method steps including provisionand/or manipulation of data may be performed by using a computer orcomputer network. Generally, these method steps may include any of themethod steps, typically except for method steps requiring manual work,such as providing the samples and/or certain aspects of performing theactual measurements.

Specifically, the present disclosure further discloses:

-   -   A computer or computer network comprising at least one        processor, wherein the processor is adapted to perform the        method according to one of the embodiments described in this        description,    -   a computer loadable data structure that is adapted to perform        the method according to one of the embodiments described in this        description while the data structure is being executed on a        computer,    -   a computer program, wherein the computer program is adapted to        perform the method according to one of the embodiments described        in this description while the program is being executed on a        computer,    -   a computer program comprising program means for performing the        method according to one of the embodiments described in this        description while the computer program is being executed on a        computer or on a computer network,    -   a computer program comprising program means according to the        preceding embodiment, wherein the program means are stored on a        storage medium readable to a computer,    -   a storage medium, wherein a data structure is stored on the        storage medium and wherein the data structure is adapted to        perform the method according to one of the embodiments described        in this description after having been loaded into a main and/or        working storage of a computer or of a computer network, and    -   a computer program product having program code means, wherein        the program code means can be stored or are stored on a storage        medium, for performing the method according to one of the        embodiments described in this description, if the program code        means are executed on a computer or on a computer network.

Summarizing the findings of the present disclosure, the followingembodiments are disclosed:

Embodiment 1: Evaluation and control unit for a gas sensor, particularlya broadband lambda probe, comprising:

pins connectable to electrical wires of electrochemical cells of the gassensor, a controller,

an ASIC reference source, wherein the ASIC reference source is operableby means of the controller,

a switch assembly connected to each of the pins, wherein the switchassembly comprises at least a first transistor, wherein a switchreference source is connected to a gate side of the first transistor andthe ASIC reference source is connected to the source side of the firsttransistor, wherein the controller is configured to vary a switchreference potential applied to the gate side of the first transistor,wherein the switch assembly is configured to allow a limited a currentflowing to the drain side of the first transistor from the ASICreference source if the potential at the gate side of the firsttransistors is at a predetermined voltage between values of an open andclosed switch over the potential at the source side of the firsttransistor.

Embodiment 2: Evaluation and control unit according to the precedingembodiment, wherein the controller is configured to switch the ASICreference potential provided by the ASIC reference source to a valuelarger than the ground of the controller while the switch assembly is inan open state.

Embodiment 3: Evaluation and control unit according to the precedingembodiment, wherein the controller is configured to put the firsttransistor in a linear mode by varying the switch reference potential inrelation to a source potential of the first transistor.

Embodiment 4: Evaluation and control unit according to any precedingembodiment, further comprising at least one comparator, wherein thecontroller is configured put the switch assembly in an open state if ashort circuit to ground is detected by the comparator.

Embodiment 5: Evaluation and control unit according to the precedingembodiment, wherein the comparator is configured to detect a shortcircuit to ground presence or absence at one of the pins if the ASICreference potential is raised and a potential at that pin exceeds acomparator threshold.

Embodiment 6: Evaluation and control unit according to any of thepreceding embodiments, wherein the switch assembly further comprises asecond transistor, wherein the switch reference source is connected to agate side of the second transistor and the ASIC reference source isconnected to the source side of the second transistor.

Embodiment 7: Method for operating an evaluation and control unitaccording to any preceding embodiment, comprising the following steps:

varying the switch reference potential applied to the gate side of thefirst transistor, in order to allow a limited current flowing to thedrain side of the first transistor from the ASIC reference source if thepotential at the gate side of the first transistor is at a predeterminedvalue between values of an open and closed switch over the potential atthe source side of the first transistor.

Embodiment 8: Method according to the preceding embodiment, furthercomprising switching the ASIC reference potential to a value larger thanthe ground of the controller while the switch assembly is in an openstate.

Embodiment 9: Method according to the preceding embodiment, furthercomprising putting the first transistor in a linear mode by varying theswitch reference potential in relation to a source potential of thefirst transistor.

Embodiment 10: Method according to any of the three precedingembodiments, further comprising detecting a short circuit to ground bymeans of at least one comparator and putting the switch assembly in anopen state if the short circuit to ground at one of the pins isdetected.

Embodiment 11: Method according to any of the four precedingembodiments, further comprising raising the ASIC reference potential anddetecting a potential at one of the pins, wherein a short circuit toground presence or absence at the one pin is detected.

Embodiment 12: Computer program configured to carry out each of thesteps of the method according to any one of embodiments 7 to 11.

Embodiment 13: Electronic storage device, on which a computer programaccording to the preceding embodiment is stored.

Embodiment 14: Electronic controller, comprising a storage deviceaccording to the preceding embodiment.

It shall be understood that a preferred embodiment of the invention canalso be any combination of the dependent claims or above embodimentswith the respective independent claim.

BRIEF DESCRIPTION OF THE DRAWINGS

Further optional features and embodiments will be disclosed in moredetail in the subsequent description of embodiments, preferably inconjunction with the dependent claims. Therein, the respective optionalfeatures may be realized in an isolated fashion as well as in anyarbitrary feasible combination, as the skilled person will realize. Thescope of the invention is not restricted by the preferred embodiments.The embodiments are schematically depicted in the Figures. Therein,identical reference numbers in these Figures refer to identical orfunctionally comparable elements.

In the Figures:

FIG. 1 shows an evaluation and operation unit,

FIGS. 2A to 2C show a switch assembly of the evaluation and operationunit according to a first embodiment in different states,

FIG. 3 shows a flow diagram of a method of the present invention,

FIG. 4 shows a switch assembly according to a second embodiment and

FIG. 5 shows a switch assembly according to a third embodiment.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of the evaluation and operationunit 100. The evaluation and operation unit 100 is configured to operatea gas sensor 200 such as a wide band lambda sensor or probe. Basically,the evaluation and operation unit 100 may be applied to any kind of gassensor such as a NOx-sensor. The evaluation and operation unit 100 isconnected by four pins RE, IPE, APE, MES to the electrical wires 201,202, 203, 204 of electrochemical cells 210, 211 of the gas sensor 200.The electrochemical cells may be a Nernst cell 210 and a pump cell 211.The wires 201, 202, 203, 204 connect the electrochemical cells 210, 211and a compensation resistor 212 of the gas sensor 200. Depending on thesensor configuration, the used wires may be different, e.g. two cellsensor with 210 and 211 and without the resistor 212, wire 204 is notpresent or one cell sensor with 211 without both 210 and 212 the wires201 and 204 are not present. Other combinations are possible as well.The evaluation and operation unit 100 is exemplified by an ASICreference source 102 to which each of the pins RE, IPE, APE, MES canindividually be connected through switches Swt_(RE), Swt_(IPE),Swt_(APE), Swt_(MES) respectively via an optional resistor 101 by meansof a controller 103. The ASIC reference source 102 is operable by meansof the controller 103. The ASIC reference source 102 may be a potentialsource. Alternatively, the ASIC reference source 102 may be a currentsource. Each of the switches Swt_(RE), Swt_(IPE), Swt_(APE), Swt_(MES)may be realized as a switch assembly 104 as will be described in furtherdetail below.

FIGS. 2A to 2C shows a switch assembly 104 of the evaluation andoperation unit 100 according to a first embodiment in different states.The switch assembly 104 is connected to each of the pins RE, IPE, APE,MES. In other words, a separate switch assembly 104 is associated witheach of the pins RE, IPE, APE, MES. The switch assembly 104 comprises afirst transistor T_(Wire) and a second transistor T_(ECU). Particularly,the drain side of the first transistor T_(Wire) is connected to the pinsRE, IPE, APE, MES. In detail, the switch assemblies 104 are realized bydiodes or transistors depending on the used semiconductor technology. Inorder to prevent a current flow in both directions typically twotransistors T_(Wire), T_(ECU) are present. This is achieved by orientingthe first transistor T_(Wire) and the second transistor T_(ECU) are inopposing directions, meaning that the parasitic diodes of the transistorare looking in opposite ways. Thereby, a current flowing between theright side, such as cables and pins, and the left side, such as themeasurement system, with respect to the illustrations of FIGS. 2A to 2Cmay be effectively stopped up to very high absolute voltages between thepin and the ECU ground, i.e. the ground potential of the controller 103.A switch reference source 105 is connected to a gate side of the firstand second transistors T_(Wire), T_(ECU). The switch reference source105 may be a potential source. Alternatively, the switch referencesource 105 may be a current source. The controller 103 is configured tovary the switch reference potential V_(SW) applied to the gate side ofthe first and second transistors T_(Wire), T_(ECU). Particularly, theswitch assembly 104 is configured to allow a limited current flowingthrough the first transistor T_(Wire) from the ASIC reference source 102if the potential at the gate side of the first and second transistorsT_(Wire), T_(ECU) is at a predetermined voltage between values of anopen and closed for switches Swt_(RE), Swt_(IPE), Swt_(APE), andSwt_(MES) over the potential at the source side of the first transistorT_(Wire). Particularly, the controller 103 is configured to set the ASICreference potential provided by the ASIC reference source 102 to a valuelarger than the ground of the controller 103 while the switch assembly104 is in an open state shown in FIG. 2B. The controller 103 is furtherconfigured to put the first transistor T_(Wire) in a linear modeprovided by the ASIC reference source 102 in relation to a sourcepotential of the first transistor T_(Wire). The evaluation and controlunit 100 further comprises at least one comparator (not shown indetail). The controller 103 is configured put the switch assembly 104 inthe open state if a short circuit to ground presence or absence isdetected by the comparator. The comparator is configured to detect ashort circuit to ground at one of the pins RE, IPE, APE, MES if the ASICreference potential is raised and a potential at that pin RE, IPE, APE,MES exceeds a comparator threshold. The operation of the switch assembly104 will be described in further detail below with reference to FIGS. 2Ato 2C.

As mentioned before, the switch assembly inside an ASIC of theevaluation and operation unit 100 consists of two transistors T_(Wire)and T_(ECU) with a common source. The function of the switch assembly104 is determined by the switch Swt_(V) which is normally in a closedstate shown in FIG. 2A. In order to set the gate-source voltage of thetransistors T_(Wire) and T_(ECU) to zero and the switch assembly 104 toopen state, switch Swt_(C) is closed when Swt_(V) is open as shown inFIG. 2B. Diodes D_(GND), D_(Wire) or D_(ECU) are intrinsic parasiticdiodes of the transistors T_(Wire) and T_(ECU). In some semiconductortechnologies some of the diodes might not be present. Forward currentthrough diodes D_(GND), D_(Wire) or D_(ECU) have to be avoided. This isrealized by opening Swt_(V) and closing switch Swt_(C). In the proposedstructure of the switch assembly 104, with switch Swt_(GND), thetransistor T_(Wire) is put into the linear mode, where it is high ohmicbut conducting, enabling current to flow from the source side to thedrain side of the transistor T_(Wire) but limiting it as shown in FIG.2C. Particularly, in applying a common gate potential V_(SW) below ECUground to the transistors T_(Wire) and T_(ECU), the total switch formedby the two transistors between the ASIC reference potential and the pin,starts conducting as shown in FIG. 2A, in contrast to when the gates ofthe transistors are not connected to any potential, as shown in FIG. 2B.This invention additional inserts the possibility to connect the gatesof the transistors T_(Wire) and T_(ECU) to a different potential, e.g.ECU ground GND, as shown in FIG. 2C. If the potential at the ECU side ofthe first transistor T_(Wire), i.e. source of the transistor, is largerthan the gate potential of the T_(Wire), e.g. ECU ground, and both arelarger than the external voltage at the drain of the first transistorT_(Wire), then the first transistor T_(Wire) is put into linear mode. Inthis mode, it is neither fully conducting nor fully open, but acts as aresistance, e.g. with 6 kΩ. This means, it allows a current through thetransistor, which is much smaller than it would be in the conductingstate. This enables charging or discharging external structures likecapacitors with time. In effect, the external voltage at the drain ofthe transistor can rise up to the newly introduced potential at thesource of the transistor, e.g. the ECU ground. Additionally, since inthis mode an internal ECU voltage is put at the source of thetransistors T_(Wire), T_(ECU), no harmful voltages appear. Thus, theinternal ECU circuitry is still protected.

The evaluation and operation unit 100 including the specific switchassembly 104 as described above allows treating the, generallytemporary, effects of short circuit to ground. The evaluation andoperation unit 100, including the specific switch assembly 104, allowsraising the voltage at an ECU pin (RE, IPE, APE, MES), if the connectionresistance to a fixed voltage source is not too low. The switch assembly104 is based on current hardware protection structure and does nothinder to pin-point the short circuit to the corresponding wire. Theachievement of raising the voltage only affected by coupling effects ofshort circuits is measureable. With the described structure, furtherquantitative measurements are allowed once the needed time has passede.g. with built-in ADC inside the chip. The structure is to be appliedto the wide band lambda evaluation circuitry, in order to allowmeasurements in the case of a short circuit of a wire to a voltage belowECU ground. In conclusion, a pin-pointing of a short circuit to groundis possible.

The method for operating the evaluation and control unit 100 will bedescribed in further detail with reference to FIG. 3 . The method can beapplied to short circuit to ground diagnosis, exemplified by thefollowing steps. In the first diagnosis step D1S1, a short circuit isdetected by additional comparators not shown in FIG. 1 : The methodstarts with a first diagnosis part at a step D1S1. If the potential atthe pin RE, IPE, APE or MES is below a threshold, e.g. ECU ground, whichis detectable by the comparator, it is concluded that a short circuit toground is present. In the other case, it is deduced that no shortcircuit is present in step D1S2 and the first diagnosis step D1S1 isperiodically repeated.

In case a short circuit to ground is found to be present, the switchesSwt_(RE), Swt_(IPE), Swt_(APE), Swt_(MES) are then opened, i.e. put inthe state shown in FIG. 2B, for protection reasons. In this state, theevaluation and operation unit 100 waits until the system hassufficiently cooled down in step D1S3.

In a second diagnosis part, the internal reference potential V_(SW) isswitched to a potential well above ECU ground while the switchesSwt_(RE), Swt_(IPE), Swt_(APE), Swt_(MES) are still opened in step D2S1.In the following step D2S2, the switches Swt_(RE), Swt_(IPE), Swt_(APE),Swt_(MES) are then put into linear mode, i.e. the state shown in FIG.2C. Conclusively, all pins RE, IPE, APE, MES which are not directlyconnected to the short circuit potential will rise, due to theresistances inside the wide band lambda sensor 200. For instance, ifwire 201 is shorted to ground, the voltage at pin RE will remain on theshort circuit potential while the pins IPE, APE and MES will rise to ECUground if the sensor resistances are large enough, i.e. if the sensor iscold enough (cf. step D1S3). Alternatively, this step D2S2 can beapplied to each pin RE, IPE, APE, MES separately.

After the pin potential is raised, the additional comparators can thenbe re-evaluated in step D2S3. If the potential at the pin RE, IPE, APEor MES has sufficiently risen, e.g. for all pins except the RE pin, thecomparators will not show a voltage too low any more. Concluding, theprotection to these specific pins RE, IPE, APE, MES are not necessaryanymore. In this case the switches Swt_(RE), Swt_(IPE), Swt_(APE),Swt_(MES) of these pins RE, IPE, APE, MES might be closed, i.e. thestate shown in FIG. 2A, in order to obtain additional data tocharacterize the short circuit in step D2S4.

The next step D2S5 concludes if the pin RE, IPE, APE or MES is uniquelyidentified. If so, this pin RE, IPE, APE or MES has been pin-pointed toin step D2S6. Whether the pin RE, IPE, APE or MES is unique, can bedetermined by e.g. by the measurement data of the closed switchesSwt_(RE), Swt_(IPE), Swt_(APE), Swt_(MES), e.g. in which direction thepin potential grows or where no data could be retrieved. If the pin wasnot uniquely identified, the system can be allowed to further cool downas in step D1S3 and/or allowed to take more time forcharging/discharging as in step D2S2.

The suggested method can be demonstrated by applying fault patterns to aproduct while studying the pin voltages at the sensor lines. In case ofthe used method the voltage at the ECU pin where the fault pattern isnot applied is raised. Insight into its data sheet can assure itscircuitry, too.

FIG. 4 shows a switch assembly 104 according to a second embodiment.Hereinafter, only the differences from the first embodiment will bedescribed and like constructional members are indicated by likereference numerals. A basic idea of the switch assembly 104 of thesecond embodiment is that if there is no requirements that a pin voltagecan rise higher than the supply voltage Vsply, it is not mandatory tohave the second transistor T_(ECU). As shown in FIG. 4 , the switchreference source 105 is connected to a gate side of the first transistorT_(Wire) and the ASIC reference source 102 is connected to the sourceside of the first transistor T_(Wire). Particularly, the switch Swt_(V)is located between the switch reference source 105 and gate side of thefirst transistor T_(Wire) while switch Swt_(GND) is arranged in parallelto the switch Swt_(V). The switch Swt_(C) can be omitted.

FIG. 5 shows a switch assembly according to a third embodiment.Hereinafter, only the differences from the first embodiment will bedescribed and like constructional members are indicated by likereference numerals. In certain technologies, it is not mandatory to usetwo transistors. They can be merged into one transistor indicated as thefirst transistor T_(Wire) with floating bulk that can be connectedeither to the left or to the right depending on which voltage is higher.As shown in FIG. 5 , the switch reference source 105 is connected to agate side of the first transistor T_(Wire) and the ASIC reference source102 is connected to the source side of the first transistor T_(Wire).Particularly, the switch Swt_(V) is located between the switch referencesource 105 and gate side of the first transistor T_(Wire) while switchSwt_(GND) is arranged in parallel to the switch Swt_(V). The switchSwt_(C) can be omitted. Further, a left switch Swt_(l) and a rightswitch Swt_(r) are shown which are connected in series with one anotherand are arranged in parallel to the first transistor T_(Wire). FIG. 5also shows the arrangement of the left switch Swt_(l) and the rightswitch Swt_(r) in parallel with respect to diodes D_(GND), D_(Wire) orD_(ECU).

1. Evaluation and control unit for a gas sensor, comprising: pinsconnectable to electrical wires of electrochemical cells of the gassensor, a controller, an ASIC reference source, wherein the ASICreference source is operable by means of the controller, a switchassembly connected to each of the pins, wherein the switch assemblycomprises at least a first transistor, wherein a switch reference sourceis connected to a gate side of the first transistor and the ASICreference source is connected to the source side of the firsttransistor, wherein the controller is configured to vary a switchreference potential applied to the gate side of the first transistor,wherein the switch assembly is configured to allow a limited currentflowing to the drain side of the first transistor from the ASICreference source if the potential at the gate side of the firsttransistor is at a predetermined voltage between values of an open andclosed switch over the potential at the source side of the firsttransistor.
 2. Evaluation and control unit according to claim 1, whereinthe controller is configured to switch the ASIC reference potentialprovided by the ASIC reference source to a value larger than the groundof the controller while the switch assembly is in an open state. 3.Evaluation and control unit according claim 2, wherein the controller isconfigured to put the first transistor in a linear mode by varying theswitch reference potential in relation to a source potential of thefirst transistor.
 4. Evaluation and control unit according to claim 1,further comprising at least one comparator, wherein the controller isconfigured put the switch assembly in an open state if a short circuitto ground is detected by the comparator.
 5. Evaluation and control unitaccording to claim 4, wherein the comparator is configured to detect ashort circuit to ground presence or absence at one of the pins if theASIC reference potential is raised and a potential at that pin exceeds acomparator threshold.
 6. Evaluation and control unit according to claim1, wherein the switch assembly further comprises a second transistor,wherein the switch reference source is connected to a gate side of thesecond transistor and the ASIC reference source is connected to thesource side of the second transistor.
 7. Method for operating anevaluation and control unit according to any preceding claim 1,comprising the following steps: varying the switch reference potentialapplied to the gate side of the first transistor, allowing a limitedcurrent flowing to the drain side of the first transistor from the ASICreference source if the potential at the gate side of the firsttransistor at a predetermined voltage between values of an open andclosed switch over the potential at the source side of the firsttransistor.
 8. Method according to claim 7, further comprising switchingthe ASIC reference potential to a value larger than the ground of thecontroller while the switch assembly is in an open state.
 9. Methodaccording to claim 8, further comprising putting the first transistor ina linear mode by varying the switch reference potential in relation to asource potential of the first transistor.
 10. Method according to claim7, further comprising detecting a short circuit to ground by means of atleast one comparator and putting the switch assembly in an open state ifthe short circuit to ground at one of the pins is detected.
 11. Methodaccording to claim 7, further comprising raising the ASIC referencepotential and detecting a potential at one of the pins, wherein a shortcircuit to ground presence or absence is detected.
 12. Computer programconfigured to carry out each of the steps of the method according toclaim
 7. 13. Electronic storage device, on which a computer programaccording to claim 12 is stored.
 14. Electronic controller, comprising astorage device according to claim
 13. 15. Evaluation and control unitaccording to claim 1, wherein the gas sensor is a broadband lambdaprobe.